The present invention relates to an image display medium, an image-forming method, and an image-forming apparatus. More specifically, it relates to an image display medium capable of repetitive rewriting, an image-forming method in which an image is formed on the image display medium, and an image-forming apparatus.
As an image display technology capable of repetitive rewriting, which is called electronic paper, technologies such as twisting of color particles (twisting ball display), electrophoresis, a thermal rewritable medium, a liquid crystal having a memory property and electrochromy have been so far known. Of these display technologies, a thermal rewritable medium and a liquid crystal having a memory property are excellent in the image memory property, but no satisfactory white display as in paper can be applied to the display surface. Accordingly, when an image is displayed, an image display portion can hardly be distinguished visually from an image non-display portion. That is, there has been a problem that the image quality is decreased.
Further, the twisting ball display has a display memory property, and oil is present only in cavities around particles inside an image display medium. However, particles are almost solid to conduct sheeting relatively easily. Even when semispherical surfaces colored in white are completely arrayed on the display side, rays entered between gaps of spheres are not reflected, and lost thereinside. Accordingly, white display with 100% coverage is theoretically impossible, and slightly grayish display is provided. Further, since a particle size is required to be smaller than a pixel size, fine particles colored in different tints have to be produced for high-resolution display, and a high-level production technology is needed.
In these technologies, as an image display medium in which an image is displayed with a toner, there is an image display medium in which a conductive color toner and white particles are contained between a display substrate and a non-display substrate that are facing each other using air as a medium to form a charge transfer layer and an electrode within both substrates (Toner Display, Nippon Gazoh Gakkai, Japan Hardcopy ""99 Ronbunshu, pp. 249-251 and Japan Hardcopy ""99 Fall Yokohshu pp. 10-13). In such an image display medium, charge is injected into the conductive color toner through the charge transfer layer, and the conductive color toner in which charge has been injected is moved by an electric field between substrates formed according to the image with an electrode, and is adhered to the display substrate. As a result, the image as a contrast between the conductive color toner and the white particles is displayed on the display substrate side.
Further, as an image display medium capable of repetitive rewriting, an image display medium using electrophoresis has been known (Kawai, Development of Electrophoresis Display Using Microcapsules, Nippon Gazoh Gakkai, Electronic Imaging Kenkyukai, p. 32, 1999).
However, in the image display technology using the toner, the contrast between black and white is low, and excellent results are not obtained in comparison with other image display technologies. Reporters of this technology presume that a conductive color toner not contacted with a charge transfer layer mounted on an inner surface of an electrode of a non-display substrate and isolated from other conductive color particles is present and charge is not injected in these isolated conductive color particles, so that the particles are not moved by an electric field but randomly remain in the substrates and the contrast is therefore low. Further, a high-speed response is also problematic.
Moreover, since the electrode is employed in the image display medium using the toner, the medium cannot directly be applied to an ordinary image-forming apparatus in which an image is formed by developing an electrostatic latent image formed on an image carrier with a toner and transferring the same onto recording paper, such as a copier or a printer.
Meanwhile, a display technology using electrophoresis or magnetic migration is a technology which provides an image memory property and in which color particles are dispersed in a white liquid. Thus, it is excellent in white display. However, since a white liquid is always incorporated into a gap between color particles in a black display portion, a grayish color is provided to decrease a contrast.
Under these circumstances, the invention has been made, and provides an image display medium which satisfies a high contrast, a safety and a high-speed response and which is capable of repetitive rewriting, an image-forming method in which an image can be formed on the image display medium, and an image-forming apparatus, and further to provide an image-forming method which can be used in a copier or a printer in which an image is formed on recording paper and an image-forming apparatus at low costs.
The image display medium includes a pair of substrates, and plural types of particle groups contained between the substrates to be movable between the substrates by an electric field applied and which are different in color and charging properties.
According to an aspect of the invention, plural types of particles different in color and charging properties are contained between substrates such that the respective particles are movable between the substrates by the electric field applied. At this time, the plural types of particles have charging properties, and the respective particles are moved according to the strength and the polarity of the electric field applied. As the particles, insulating particles to be charged through frictional charging or conductive particles to be charged by injecting charge through an electrode may be used.
Incidentally, during studies for making the invention, the present inventors have presumed the following with respect to the problems of the display medium using the toner. That is, the image display medium using the toner is so adapted that white particles are treated as a stationary medium unreactive with an electric field and conductive black particles are caused to migrate therein. For this reason, it is only one (conductive black particles) of the two particle groups that can be moved between the substrates. Specifically, white particles can be fixed in nearly stationary state by a structure that the white particles are packed well between the substrates. Nevertheless, in this construction, conductive black particles have to be moved in high-density white particles. Further, the conductive black particles hardly exclude the white particles remaining near the surface of the substrate. Thus, only grayish display is conducted to decrease the contrast.
Moreover, in case of using conductive particles, particles that are not directly contacted with a charge injection electrode have no chance of charge injection unless they are contacted with other charged conductive particles. Thus, such particles cannot be reacted with an electric field. That is, it is presumed that when conductive black particles having good charging properties are used but stationary white particles are present, almost all of conductive black particles cannot be moved and contributed to image display.
In the invention, therefore, the image display medium is so constructed that the particles belonging to the different particle groups can be moved between substrates in mutually opposite directions by the electric field applied. Further, since charging properties of these particles are different depending on the particle group, the moving characteristics by the electric field are also varied.
In case of using insulating particles of reverse polarities, the particles are in the mixed state by the Coulomb force between the substrates just before being contained, and the particles of reverse polarities are separated by applying electric fields stronger than the Coulomb force between these particles, moved in the directions of the electric fields of reverse polarities, and adhered to the surfaces of the substrates. Even when the electric fields are broken, the particles are retained on the substrates by the image force and the van der Waals force. The respective particle groups are accumulated on the respective substrates. In reality, with respect to the applied voltage in the rewriting, an external force stronger than the image force and the van der Waals force can be applied.
In case of using conductive particles, when the particle groups are movable between the substrates, the conductive particles are also moved well, and a rate at which the particles are contacted with each other is increased to increase a rate at which to supply charge to uncharged particles present between the substrates. As a result, the movement of these particles by the electric field can be started.
Particles having the same polarity but different in charging properties and therefore different in the response to the electric field ought to have a high fluidity between particles owing to the same polarity. However, when the particles are packed at high density, these are sometimes agglomerated by the van der Waals force. In the invention, since the particles are contained to be movable between the substrates according to the direction of the electric field, the movement of the particles is smoothly conducted to allow the image display with a good response. In this case, the particles with a large amount of charge are first adhered, and the particles with a small amount of charge are then adhered by increasing the electric field, whereby the color can be changed.
As the other combination, a combination of conductive particles and insulating particles and a combination of two types of conductive particles having different conductive characteristics, namely, a hole type and an electron type, are also available.
In using either of these particle combinations, it is advisable that at least two types of the particle groups have charging properties of different polarities. As stated above, since the two types of the particles have reverse polarities, the respective particles are moved in the reverse electric field directions to provide quite a good response. Moreover, since the particles are clearly separated according to the polarities, the contrast or the sharpness of the image is improved. Especially when white particles and particles of another color which are charged in reverse polarities are used, an image can be displayed as if it is printed on paper.
When the particles of reverse polarities are insulating particles, frictional charging occurs between particles in the movement by the electric field to increase the amount of charge. Accordingly, an effect of improving the image memory property in the absence of the electric field is brought forth.
Incidentally, xe2x80x9cmovable between the substratesxe2x80x9d here referred to means that the particles present on one substrate side can be moved to another substrate side by applying the electric field. It includes not only a case in which the particles of all the particle groups are moved by the electric field at the same time but also a case in which the particles of some particle group are not moved by some strength of the electric field, but can be moved by increasing the strength of the electric field. That is, when the particles are contained in this state, the movement of the particles is substantially not inhibited by the presence of the particles of the other type of the particle group.
Further, for the particles of the various types to be movable between the substrates, any one of, or a combination of, the filling rate of the particles in the substrates, the fluidity between the particles, the form of the particles, the particle diameter, the material of the particles and the substrate inner surface (electrode surface when the particles are directly contacted with the electrode) may be determined. The following are especially preferable.
When the filling rate of all particles contained between the substrates is at least 0.1 vol. % and at most 50 vol. %, the image display is enabled. When it is 40 vol. % or less, especially 25 vol. % or less, the image contrast is good. Thus, it is preferable. When it exceeds 50 vol. %, the particles become abruptly compact to start inhibiting the movement thereof. Thus, a rate of particles remaining on one substrate side is increased to decrease the contrast. When it is at most 50 vol. %, the particles can be moved between the substrates.
The higher fluidity between the particles is preferable. Accordingly, an external form of particles is preferably a curved form, more preferably an elliptic form, further preferably a spherical form. For increasing the fluidity, an external additive to decrease a frictional force may be used.
A particle diameter in which particles can be moved by the electric field applied is available. An average particle diameter is preferably 1 xcexcm or more. When it is less than 1 xcexcm, the van der Waals force is greater than the Coulomb force as a binding force between the particles or between the particles and the substrates. Thus, in this state, the particles of reverse polarities are hardly separated by the electric field. However, when particles are adapted to be separated by combination with a force other than the electric field, such as a force of ultrasonic vibration, particles having a particle diameter of less than 1 xcexcm can sometimes be used. Especially, when a high image memory property is required, it is advisable to make the particle diameter less than 1 xcexcm. When a rewriting device is simplified or rewriting is conducted at high speed, it is advisable to employ a particle diameter of 1 xcexcm or more.
With respect to a combination of the particles and the substrate materials or the portions in contact with the particles, such as the electrode, it is advisable to select a combination which decreases the adhesion therebetween because the particles can easily be moved between the substrates. Thus, it is preferable in the rewriting at high speed. The surface of the substrate may be a flat surface or a scattered surface (especially an observation surface of the substrate on the reverse side).
It is also possible that a transparent insulating solvent is poured between the substrates to move two or more color particles electrophoretically. This is because the image contrast can be increased in comparison with the electrophoresis of color particles in an ordinary white insulating liquid.
However, since the movement of the particles is inhibited by the viscosity of the solvent, the high-speed response is decreased, and the color of the color particles on the reverse side is sometimes faded by refraction and scattering of the incident light due to the solvent. Accordingly, in consideration of the ease of handling in vacuum, in use or in production, it is most preferable that the various particle groups are contained in a gas such as air.
As a method of charging the particles, the particles can be charged by the electric field after being contained, or the plural types of the particle groups can previously be charged by mixing and then contained between the substrates. Further, in case of the insulating particles, it is also possible that after the particles are contained, the display medium itself is shaken to stir and frictionally charge the particles, whereby the particles are charged in reverse polarities.
The average amount of charge (femto Coulombs, hereinafter referred to as fC per particle) of the particles is approximately in proportion to a square of the average particle diameter 2r of the particles. The smaller the average particle diameter, the smaller the average amount (fC per particle) of charge. It is thus found that the preferable range of the average amount of charge varies depending on the particle diameter. That is, the average amount of charge of each particle is preferably at least xc2x15xc3x97(r2/102) fC per particle and at most xc2x1150xc3x97(r2/102) fC per particle. When it is smaller than xc2x15xc3x97 (r2/102) fC per particle, particles are separated, and moved between the substrates in the different directions, but no satisfactory display density is shown. Further, when it is larger than xc2x1150xc3x97(r2/102) fC per particle, the particles are not separated, and these are formed into an agglomerate, and moved in the same direction to decrease the contrast of the display density. The charging properties of the particles can be controlled by the material constituting the particles, the external and internal additives added to the particles, the layer structure of the particles and the form of the particles.
According to another aspect of the invention, an additive is incorporated in the surfaces of the particles of at least one type of the particle groups, and the additive contains a titanium compound obtained by the reaction of TiO (OH)2 and a silane compound, whereby an appropriate amount of charge, a stable charge retention and a good fluidity are imparted to the particle groups. Consequently, the particles can smoothly be moved stably between the substrates by the electric field applied therebetween without strongly adhering the particles to the inside surfaces of the substrates, and the image display is enabled with a high contrast.
As a result, the electric field is applied according to the image to move the particle groups according to the image, and the image can be displayed by the contrast of colors of the particle groups. Further, even when the electric field is lost, the particle groups moved onto the substrates can remain there by the image force and the adhesion to retain the image. After the lapse of time, the electric field is applied again, and the particles group can then be moved again. In this manner, the image can be displayed repetitively by applying the electric field from outside according to the image. By the way, at least two types are sufficient as colors of the particle groups. The charge-transporting property may be imparted to the particle groups. Further, an insulating material such as a dielectric, a conductive material and a charge-transferring material can be used in the pair of substrates. A combination of particles having a contrast, namely, capable of image display and substrates is shown in a table in FIG. 43.
In the table, a blank indicates a combination having no contrast, namely, incapable of image display.
The symbols in the table are described below. A, B and C refer to a process for charging particles.
A: First and second particles are moved according to the electric field between members by being reversely charged in advance through frictional charging, and are adhered to the opposite members to give a contrast.
B: First or second particles are moved by the electric field between the members by being charged through injecting charge therein from the substrate. The other particles are moved according to the electric field between the members by being charged by the friction through the movement of the former particles or the previous friction through stirring or vibration.
C: Both the first and second particles are moved according to the electric field between the members by being charged through injection of charge from the substrate.
Further, a prime (xe2x80x2, Bxe2x80x2 or Cxe2x80x2) allotted to B or C indicates from which member charge is injected in particles.
B or C without a prime indicates that charge is injected in the particles from both of the first and second members.
Bxe2x80x2 or Cxe2x80x2 indicates that charge is injected in the particles from one of the members.
Further, figures encircled indicate with what behavior the particles have a contrast when the electric field is applied between the members.
A: The first and second particles have a contrast by being adhered to opposite members.
B: Conductive particles in which charge is injected by the members are moved between the members by being charged through injection of charge from both the members. As soon as the electric field is lost, the particles are adhered to the members, so that half of the particles are adhered to each of the members. However, since charge is injected in the other particles from one member, the particles are adhered to one member by the electric field to give a contrast.
X: The conductive particles are always adhered to the same member regardless of the polarity of the electric field. The other particles are moved according to the polarity of the electric field between the members. Consequently, a contrast is given according to the amounts of the other particles adhered.
With respect to the particles having the hole-transporting property, the electron-transporting property and the conductivity in the blank of the table, when the frictional charging occurs by the mixing and stirring of the first and second particles to charge the same in opposite polarities and the charges of both the particles are neutralized through injection of charge received from the substrate or through contact between both the particles or the particles are not charged in the same polarity, this does not apply, and a contrast is given.
According to another aspect of the invention, the particles can be moved with a magnetic force by using magnetic particles in at least one of the particle groups.
Further, spacer particles having a larger particle diameter than these particles may be contained between the substrates. As a result, a distance between the substrates can be maintained approximately constant.
According to another aspect of the invention, the substrates have a cell structure partitioned in a predetermined shape, whereby the distance between the substrates can be maintained approximately constant and partial imbalance of the particles contained between the substrates can be controlled to allow more stabler image display.
According to another aspect of the invention, the particle groups may be encapsulated in cells according to plural colors forming a multicolor image. For example, yellow particles and white particles, magenta particles and white particles, and cyan particles and white particles are encapsulated in the respective cells. The color image can be formed by generating the electric field according to each color.
According to another aspect of the invention, there is provided an image-forming apparatus in which the image is formed on the image display medium, the image-forming apparatus having an electric field-generating unit for generating an electric field adapted to the image between the pair of substrates.
In this case, the electric field-generating unit generates the electric field adapted to the image between the pair of substrates, whereby charged particle particles between the substrates which are previously charged or remain charged after the image formation is once conducted can be moved according to the image. Further, according to another aspect of the invention, when the matrix electrodes are formed on the pair of substrates, the electric field adapted to the image can be generated by applying a voltage adapted to the image to the matrix electrodes.
For example, it is possible that a pair of stripe electrodes are crossed to provide an electrode arrangement by a so-called simple matrix structure and the electric field is thus applied between the substrates to move the particles. Plural stripe electrodes may be placed on the substrates or held inside the substrates. This simple matrix structure can reduce production costs because the electrode structure is simple and the production is easy.
Further, according to another aspect of the invention, when a pixel electrode is formed on one of the pair of substrates and an electrode is formed on another substrate, the electric field adapted to the image can be generated by applying a voltage adapted to the image to the pixel electrode.
The electric field-generating unit may be an ion-generating unit or a stylus electrode.
According to another aspect of the invention, there is provided an image-forming apparatus for forming an image on an image display medium in which a photoconductive layer is formed on one of the pair of substrates, the image-forming apparatus having electrodes for applying a voltage between the pair of substrates, a transparent panel formed in a pattern adapted to the image and a light source for applying light to the transparent panel.
In this case, the voltage-applying unit applies the voltage between the pair of substrates. For example, an image display medium in which a photoconductive layer is formed on one of the pair of substrates or an image display medium in which at least one of the particle groups contains a photoconductive material is held between substrates having electrodes, and, for example, a DC voltage is applied thereto. A transparent panel formed in a pattern adapted to the image is attached to the substrate on which the photoconductive layer is formed, and this transparent panel is irradiated with light or exposed to light from the light source. The photoconductive layer here acts as a dielectric layer in an unexposed state, and as a conductive layer in an exposed state. Accordingly, in the exposed state, the particle groups between the substrates are moved according to the image by the voltage applied by the voltage-applying unit to form the image.
According to another aspect of the invention, there is provided an image-forming apparatus for forming an image on an image display medium, the image-forming apparatus having a latent image carrier, an electrostatic latent image-forming unit for forming an electrostatic latent image adapted to the image on the latent image carrier, and a counter electrode for generating an electric field between it and the latent image carrier, the counter electrode being mounted in a position facing the latent image carrier such that the image display medium can be positioned therebetween.
In this case, the electrostatic latent image-forming unit forms the electrostatic latent image adapted to the image on the latent image carrier. The counter electrode is mounted facing the latent image carrier such that the image display medium can be positioned therebetween. That is, the electric field can be generated between the electrostatic latent image on the electrostatic latent image carrier and the counter electrode. Consequently, the particle groups contained between the substrates can be moved according to the image by the electric field generated to form the image on the image display medium. When the electrostatic latent image for each color is formed on the latent image carrier and the foregoing image display medium is used, the color image can also be formed.
The electrostatic latent image-forming unit may be so adapted that the latent image carrier having a photoreceptive layer and uniformly charged may be scanned with light beam adapted to the image to form the latent image adapted to the image on the latent image carrier. Further, the latent image carrier may be irradiated with ions generated by the ion-generating unit to form the electrostatic latent image adapted to the image on the latent image carrier. Still further, the electrostatic latent image adapted to the image may be formed on the latent image carrier by applying a high voltage to the stylus electrode to generate charge adapted to the image.
According to another aspect of the invention, a bias voltage is applied to the counter electrode, whereby an electric field can be generated in the opposite direction between the latent image carrier and the counter electrode. Therefore, for example, the particles adhered to the substrate on the counter electrode side can be moved to the substrate on the latent image carrier side, and the particles adhered to the substrate on the latent image carrier side to the substrate on the counter electrode side respectively.
According to another aspect of the invention, the image-forming apparatus has further an inputting unit for inputting whether the medium on which the image is formed is the image display medium or an image-recording medium, a developing unit for developing the electrostatic latent image formed by the electrostatic latent image-forming unit with a toner when the result inputted by the inputting unit is the image-recording medium, a transferring unit for transferring the toner image developed by the developing unit onto the image-recording medium, and a fixing unit for fixing the toner image transferred onto the image-recording medium.
In this case, the inputting unit is for inputting whether the medium on which the image is formed is the image display medium or the image-recording medium, namely, ordinary recording paper. For example, a keyboard or a mouse can be used. Users can select the medium by this inputting unit. Further, the inputting unit may be a medium-detecting unit for detecting whether the medium on which the image is formed is the image display medium or the image-recording medium. In this instance, it is possible to detect which the medium is from an amount of reflected light by irradiating the medium with light. Moreover, it is also possible to detect which the medium is by detecting the weight.
In the developing unit, the electrostatic latent image formed by the electrostatic latent image-forming unit is developed with the toner when the result inputted by the inputting unit is the image-recording medium, namely, ordinary recording paper. In the transferring unit, the toner image developed with the developing unit is transferred by applying, for example, a voltage to the image-recording medium. In the fixing unit, the toner image transferred onto the image-recording medium is fixed through, for example, heat fixing or pressure fixing.
Further, the transferring unit may be a counter electrode. That is, the image formation of the image display medium and the image formation of the image-recording medium can be conducted with the same transferring unit, whereby the apparatus can be simplified and the costs be reduced.
When the medium is the image display medium, the fixing treatment is dispensed with. Thus, according to another aspect of the invention, it is also possible that when the result inputted by the inputting unit is the image display medium, the fixing treatment by the fixing unit is not conducted. Consequently, the deterioration of the image display medium owing to heat can be prevented.
According to another aspect of the invention, the apparatus has further a development stopping unit for stopping the development by the developing unit when the result inputted by the inputting unit is the image display medium.
In this case, the development stopping unit stops the development when the result inputted by the inputting unit is the image display medium because there is no need to operate the developing unit. Further, when the developing unit is in an operable state, the toner on the electrostatic latent image carrier is supplied, and the image display medium is sometimes contaminated with the toner. Accordingly, when the development with the developing unit is stopped, the adhesion of the toner to the image display medium can be prevented.
In the development-stopping unit, the developing unit may be spaced apart from the latent image carrier, whereby the supply of the toner to the electrostatic latent image carrier can be prevented. Further, the rotation of the toner carrier included in the developing unit may be stopped. Still further, a voltage of reverse polarity to the potential of the electrostatic latent image may be applied to the toner carrier included in the developing unit. Furthermore, the supply of the toner to the toner carrier included in the developing unit may be stopped.
According to another aspect of the invention, the apparatus has further a charging unit for preliminarily charging the particle groups.
In this case, the particles can satisfactorily be moved by preliminarily charging the particle groups with the charging unit to display the image stably.
In the charging unit, at least one of a DC voltage and an AC voltage is applied to the substrates. When the DC voltage is applied to the substrates, the particle groups can uniformly be adhered to one of the substrates. Thus, there is no need to apply bias to the counter electrode. Further, when the AC voltage is applied, the particle groups can satisfactorily be charged. Still further, the charging unit may be a vibration unit for vibrating the substrates. Furthermore, when the image display medium in which at least one of the particle groups is magnetic is preliminarily charged, the charging unit may apply an alternating magnetic field to the substrates.
According to another aspect of the invention, there is provided an image-forming method which includes applying an alternating field to plural types of particle groups of an image display medium contained between substrates to be movable between the substrates by an electric field applied and which are different in color and charging properties just before an electric field adapted to an image information is applied, at least two types of the particle groups being different from each other in charging properties. Consequently, since the particles are forcibly vibrated between the substrates just before the image display, the particles adhered to the surfaces of the substrates are peeled off to expedite the movement of the particles adapted to the image.
According to another aspect of the invention, the alternating field is applied to the whole surface of the image display medium at the same time just before applying an electric field adapted to the image information, whereby the particles in the substrates can be moved for a short period of time. This is effective for moving the particles by applying the electric field between the substrates using an electrode of a character or a pattern or for moving the particles by applying the electric field between the substrates using an electrode of a matrix structure.
According to another aspect of the invention, the alternating field is applied just before applying the electric field adapted to the image information according to a sequence for applying an electric field of a line unit with a matrix electrode, whereby the particles are forcibly vibrated on the whole surface just before the image display without applying a new sequence or wiring for sending a signal of whole surface simultaneous driving. Accordingly, the movement of particles adapted to the image can be expedited with only a device required for the image display without providing an additional special device.
According to another aspect of the invention, the amplitude of the alternating field is reduced with the lapse of time, whereby the increase in the moving rate accompanied by the increase in the amount of charge due to the frictional charging of the particles is prevented, and the movement rate of the particles reciprocated is gradually reduced to zero to decrease the adhesion between the particles or between the particles and the substrates. Consequently, the particles can easily be moved according to the electric field.
According to another aspect of the invention, the voltage waveform of the alternating field is rectangular. As a result, a force to act on the particles by the electric field for a unit time is increased to increase the response to the electric field. Thus, the particles can be moved to the opposite surface for a shorter period of time.